1. Field of the Invention
The present invention concerns an expansion device for the coolant/insulating fluid in an x-ray apparatus as well as an x-ray radiator with such an expansion device.
2. Description of the Prior Art
In a medical x-ray apparatus, to reduce the heat that accumulates due to the generation of x-ray radiation it is necessary to provide cooling for the x-ray tube arranged in an x-ray radiator. For cooling it is known to surround the x-ray tube with a coolant which can (as, for example, insulating oil) exhibit insulation properties. The coolant and/or insulation must exhibit a pressure that is high enough to prevent an outgassing, since otherwise the cooling capacity and/or the ability to withstand electrical voltages are reduced, but is low enough to prevent damaging of the x-ray tube due to overpressure.
For this purpose, expansion devices are known that ensure a defined minimum pressure for the coolant and/or insulation means and allow an expansion (caused by a temperature increase) of the coolant and/or insulation within a defined range. Particularly in the case of x-ray apparatuses with rotary piston x-ray tubes rotating in coolant and/or insulation, negative pressure can be created due to the rotation movement. Such known expansion devices are formed by a reservoir in which the coolant and/or insulation means is located and a sealed air chamber (such as, for example, an airbag or a metal bellows) is provided to ensure the minimum pressure. An expansion of the coolant and/or insulation compresses the sealed air chamber, leading to an excessive, exponential increase of the pressure. If the pressure rises too high, the x-ray apparatus is deactivated (triggered by a pressure switch).